TEMPORAL VARIATION OF RA-228 IN THE NEAR-SURFACE GULF OF MEXICO

The Mn-fiber technique for extracting radium from seawater has proved useful for studying the marine geochemistry of 228Ra. In the Gulf of Mexico, this technique was used to measure the surface and near-surface distribution of 226Ra and 228Ra. The observed surface distribution of 228Ra, and particularly the radium activity ratio (228/226) can be explained by known circulation patterns, or, when local surface currents are not well understood, may provide insight into their general characteristics. The radium activity ratio has increased from 0.5 in 1968 to 0.7 in 1973 in the surface Gulf of Mexico. This observed increase cannot be attributed to known anthropogenic or natural source perturbations within the Caribbean Sea-Gulf of Mexico system. Possible causes include a change in the residence time for near-surface water, or variations in the relative dominance of the two sources for water entering the eastern Caribbean; the North Equatorial Current and the Guiana Current. The temporal distribution of 228Ra is unstable and naturally variable over a time period less than or equal to five years in the Gulf of Mexico and by extrapolation, the Caribbean Sea. Therefore, its usefulness in calculations of eddy diffusion coefficients for these regions is greatly diminished. © 1979.